In recent years, there has been a growing demand for information processing devices that meet various requirements for the extensively and highly advanced information society. In particular, hard disk drives and magnetoresistive random access memories (MRAMs) are memory devices based on magnetic moments of ferromagnetic materials. Such spin-electronic devices using spin degree-of-freedom of electrons are suitable for increasing integration by downsizing memory cells, operable at high speed, and nonvolatile. Hence their use will further expand in memory apparatuses and other applications. As one of controlling methods for a magnetization direction of small magnetic elements in spin-electronics devices, the use of a current-induced spin transfer phenomenon has been known. The “spin transfer” refers to the transfer of angular momenta from spins of conduction electrons to localized magnetic moments in the magnetic elements. In contrast to the scheme based on magnetic field applications, the spin transfer scheme is characterized in that a write-in current can be reduced with downsizing magnetic memory cells.
The technical subject about the spin transfer write-in for a magnetic element using perpendicularly magnetizable materials has been disclosed in Japanese laid-open patent application JP-A 2004-193595 (Kokai). An as-deposited multilayer film with a magnetic fixed layer (hereinafter referred as a “fixed layer”), an intermediate layer and a magnetic free layer (hereinafter referred as a “memory layer”) laminated is patterned into dots, each being tens to hundreds of nanometers square to be a magnetic element. The shape of the magnetic element adapted to the spin transfer write-in is illustratively a pillar dot. Passing a current through the multilayer film in the direction perpendicular to the film surface provides control (write-in) and detection (read-out) of the magnetization of the memory layer, leading to use of the element as a magnetic memory element.
The use of perpendicularly magnetizable materials provides the memory element with thermal stability, eliminating needs of shape anisotropy, the magnetic memory element thus being suitable for high integration. The magnetic memory element using perpendicularly magnetizable materials adapted to the spin transfer write-in tends to reverse its magnetization efficiently when providing the memory element with two fixed layers per a memory layer. Adjusting one of the two intermediate layers and the other to a barrier layer and a conductive layer, respectively, differentiates the currents over positive/negative directions for the magnetization reversal of the element. Such asymmetry of reversal current enlarges only a one-direction current, increasing a break-down risk of the memory element. The asymmetry also lowers the other direction current, creating a risk of a wrong write-in at the time of read-out. A magnetic memory apparatus using such elements must be provided with several power supplies corresponding to each greatly different reversal current value, possibly resulting in a cost overrun.
U.S. Pat. No. 6,967,863B-2 discloses a technical subject about a magnetic element adapted to the spin transfer write-in using perpendicularly magnetizable materials, but does not refer to the above-mentioned asymmetry or an answer to it. A magnetic element using perpendicularly magnetizable materials is disclosed in Japanese laid-open patent application JP-A 2007-142364 (Kokai).